The present invention relates generally to packaging and packaging materials, and more particularly to a packaging material for food products wherein the packaging material comprises a paperboard substrate having a first surface to which there has been applied a coating suitable for printing high quality graphics. Such substrates are known in the art as coated-one-side or C1S paperboard substrates. The invention further relates to the application of a barrier material to the opposite or uncoated surface of such substrates which is resistant to the penetration of moisture and moisture vapor. Compositionally, coatings useful for printing high quality graphics generally include a fluidized blend of minerals such as coating clay, calcium carbonate, and/or titanium dioxide with a suitable binder such as starch, polyvinyl alcohol, polystyrene or the like. These coatings are generally applied to paperboard substrates on a papermachine during the papermaking process by typical coating devices such as roll, rod, air knife or blade coaters. Successive densification and polishing of the coated surface by calendering finishes the surface to a high degree of smoothness and gloss to achieve a superior surface for high quality printing.
Meanwhile, barrier materials for application to the opposite surface of C1S paperboard substrates, for protecting the substrates from moisture or the penetration of moisture vapor include extrudable resins such as low density polyethylene (LDPE), polypropylene (PP) and polyethylene terephthalate (PET). However, the use of extrudable resins for the intended purpose must be done in a separate process, that is generally remote from the papermachine, which entails increased costs and handling. Moreover, the use of extruded resins for moisture vapor barrier protection generally requires a thick film to achieve the desired results. Suitable and effective moisture barrier protection can be achieved for C1S paperboard substrates with the use of coatings prepared from emulsions such as acrylics, ethylene vinyl chloride (EVCL), polyvinylidene chloride (PVDC) and PET. Such coatings can be applied in a uniform and continuous film using the same coating devices used on a papermachine such as roll, rod, air knife or blade coaters, however the application of such coatings on a papermachine is generally not done because of the high costs associated with small orders, and the high speed of papermachines.
In order to overcome these and other problems, the method disclosed in U.S. Pat. No. 5,418,008 was developed. According to the teachings of the '008 patent, a paperboard substrate which has been previously coated on one or both surfaces is applied with a continuous film of a barrier material, at a low coat weight, in a single pass, on a printing press, at the same time that the substrate is printed and converted into blanks for forming packages. Unfortunately the practice of the invention disclosed in the '008 patent, which is assigned to the present assignee herein, has been discouraging due to poor coating holdout, drying problems and high coating consumption, particularly with the use of C1S paperboard substrates. Accordingly, the present invention was designed to improve upon and overcome any problems with the practice of the invention disclosed in the '008 patent.